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 25-28 September, 2018 | Singapore
such as dilute (1%) phenylephrine. By contrast, episcleral vessels are larger, branch less, appear to “stop short” of the limbus, and blanch more slowly, if at all, with topical vasoconstrictors.
Potential Clinical Diagnoses in Reddened Eyes Since superficial vessels indicate superficial disease and deep vessels indicate deeper disease, it is possible
to compile a list of potential likely causes of red eye
in association with deep vascular injection (Orbital disease, deep keratitis, uveitis, glaucoma, or – rarely
– scleritis) or superficial vascular injection (blepharitis, conjunctivitis, or superficial keratitis). This list guides diagnostic testing and ensures that painful, vision- threatening or potentially life-threatening diseases are not written off simply as conjunctivitis. The only confusion in this list is brought about by the principle of “innocent bystander” inflammation discussed earlier. Subtle (early) glaucoma, orbital disease, or uveitis can cause only mild conjunctival hyperemia before they progress to a stage where they cause episcleral hyperemia.
Diagnostic Tests for "Every" Red Eye
The following is a brief outline of the diagnostic tests that should be considered for all cases of reddened eye.
Retroillumination is a simple but extremely useful technique for assessment of reddened eyes. A focal light source held close to the examiner’s eye and directed over the patient’s nose from at least arm’s length is used to elicit the fundic reflection. Each eye is illuminated equally and the fundic reflex is used to assess and compare pupil size, shape, and equality. Some general rules help interpret retroillumination findings:
· Conjunctivitis – never associated with anisocoria
· Uveitis – often associated with miosis
· Glaucoma – often associated with mydriasis
The Schirmer tear test (STT) should be performed on all reddened eyes but especially those in which there
is mucoid discharge. The only exception is those with an obvious deep ulcer in which this test may be unsafe. Normal STT values for dogs are > 15 mm in 60 seconds. However STT values in normal cats range widely (3-32 mm; mean = 17 mm in 60 seconds) and are more difficult to interpret than in dogs.
Tonometry or measurement of intraocular pressure (IOP) is essential in every reddened eye except those at risk of rupture. Its use will permit differentiation of the two major, vision-threatening conditions in which red-eye is the hallmark feature – uveitis (in which IOP tends to be low) and glaucoma (which is defined by elevated IOP)
– from conjunctivitis (in which the IOP will be normal). Across large populations, normal canine and feline IOP is reported as 10-25 mmHg. However, some variation occurs. Comparison of IOP between right and left eyes permits application of a reasonable rule of thumb that
IOP should not vary between eyes of the same patient by more than ~20%. Perhaps the most important role for tonometry is the monitoring of progress of these diseases and the titration of medications needed.
Aqueous flare occurs as a result of breakdown of the blood-ocular barrier with subsequent leakage of proteins into the anterior chamber. Therefore, is a pathognomonic sign of uveitis and must be performed in every reddened eye. It is best detected using a very focal, intense
light source (the small circular aperture on the direct ophthalmoscope works well) in a totally darkened room. The passage taken by the beam of light is viewed from an angle. In the normal eye, a focal reflection is seen where the light strikes the cornea. The beam is then invisible as it traverses the almost protein- and cell-free aqueous humor in the anterior chamber but becomes visible again as a focal reflection on the anterior lens capsule and then as a diffuse beam through the body of the normal lens. If uveitis has allowed leakage of serum proteins into the aqueous humor, then these cause a scattering of the light as it passes through the anterior chamber. Aqueous flare is therefore detected when the beam of light is visible traversing the anterior chamber.
Application of fluorescein dye to the cornea should be routinely used in all reddened eyes to diagnose corneal ulcers. It should be performed after all other parts of the exam are completed so as not to alter the STT result or affect visualization of other structures.
Retropulsion of the globe is a simple but useful method for investigating orbital disease. This is performed by applying gentle digital pressure to both globes through closed eyelids. The resistance to retropulsion and the resilience with which the globes “spring” back against the retropulsive force are subjectively assessed. Retropulsion of the globe in a variety of directions may further localize orbital masses or outline smaller masses that would be missed by direct caudal retropulsion only. This should not be done in eyes at risk of rupture.

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